In this, I will show you how to get an amazing background just like this one. Enjoy!
Step 1: Select
First select your image from the browser that you are using.
Step 2: Save
Once you have selected the image, right click, and press "save as".
Step 3: Prepare
Go to your desktop and right click, then press "new wallpaper".
Step 4: Select
Once you have pressed "new wallpaper" select your image.
Step 5: Enjoy
Enjoy your new rainbow background!